Finished rereading this great classic. Larry Niven’s take on Dyson spheres is as follows: A sphere is pretty hard to build. Why not make a ring? A million miles wide with mountains on both sides to keep the air in. Leave the open end facing the sun, and construct the ring at roughly Earth’s orbital equivalent. Spin it at 700 some mile per second to create a gravity, and Voila!
Assuming you could build it though, would it stay in place? Wouldn’t it get out of kilter and vibrate like hell (spin a hoop on the ground and see what I mean?)
Given the materials, would the physics allow it to exist?
Therein lies the problem. Earth holds together by its own gravity. The Ringworld would have to be built out of riveted steel girders or something along its entire circumference. And if one part of one section were just a little bit weak, fwoom, you’d fall through the floor, all the air would rush out after you, and the rest of the ring would be thrown off-kilter. Said off-kilterness may just cause a precession, but it may also be dynamically unstable (i.e. each wobble amplifies itself with each oscillation until one end of the hoop bangs into the sun).
Didn’t he address the instability in a later book, though? IIRC, there was some sort of automatic corrective system (little jets?) that would move the Ringworld back into a stable orbit if it got knocked off kilter. Otherwise, that whole Fist of God impact that made the giant mountain would have doomed it.
Oh, you have no frikkin imagination. Build a ringworld with a “roof” (inner ring) to make it all airtight. Each section could have an airlock, so if one breaks, you just close the lock, and the off-kilterness could be easily compensated for by thrust engines evenly spaced along the ring.
Yes, but then you’ve created a gigantic spaceship, versus an artificial world. Not that that’s a bad thing mind you…
As for it being corrected, yes there are a seies of attitude jets along the rim, and in the sequel, Ringworld engineers, this subject is dealt with. There is also a 3rd book that I have not read yet called Ringworld throne.
The Ringworld in the original book is unstable, which was proven by a ton of college eggheads… he also addresses the issue in either N-space or Playgrounds of the Mind.
To expand on Tristan’s answer, according to those eggheads the Ringworld was stable except along its plane. That is, it would not vibrate up and down ( when viewed from its side ) so that Scylla’s spinning hoop on the ground is not quite an accurate picture. Rather it would slide around the sun like a hula hoop around a person’s body. Sections of the ring would get closer and then farther from the sun until eventually part of the ring collided with it.
That would be bad, he understated.
As has been stated, the Pak built attitude jets to deal with this.
Specifically, it’s unstable in the plane of the elliptic. That is, it’ll be inclined to drift into its star without lots of help. At a con this past august, Niven got together with George Dyson (Freeman’s son) and Robert Forward and figured out that even if the Bussard ramjet could exist, it wouldn’t be able to gather enough H[sub]2[/sub] at the Rims to maintain the Ring’s orbit.
Tracer, the integrity issue was wished away by magic. Niven figured that if he could propose a spacefaring species advanced enough to build the Ring (not to mention all its incorporated systems), they could figure out how to create a pseudometallic hull material sturdy enough to withstand the gees (and most meteor holes). Scrith (the hullmetal) blocked something like 40% of neutrinos, making it something like 40% as dense as neutrnoium.
But hey, a sf writer’s allowed a little deus ex machina.
What would happen if you jump? Surely if the only “gravity” is that created by centripetal acceleration, you’d go floating off quite differently than if you were on a planet. I think I can picture that the ground would eventually meet up with you. But what if you hit a golf ball? Also, you’d get different drive lengths if you were facing different ways along the rotational axis.
At one point, the year Ringworld came out during a SF convention, about 200 MIT students started a chant of “THE RINGWORLD IS UNSTABLE!” and kept it going for about twenty minutes IIRC.
edwino, centripetal force creates reactional (or relative) gravity, so if we were dealing with light building material and an extremely “fast” spin, you would for the most part be correct. However, this puppy was supposed to be huge, so the mass of the ring would create gravity relative to its mass and relative acceleration.
Yup, ChingaQueso’s dead on–we’re talking mind-numbingly huge scale here. Local gravity would behave essentially identically to a gravity well. Local in this case is something on the order of hundreds of miles (maybe thousands–I may have dropped a zero in there). That is, if you have a big enough object falling onto the Ring, it’ll behave oddly as it falls, drifting sideways. But the object has to be reeeeallly big.
Yes, the Ringworld is too big for noticeable coriolis effects.
The Ringworld Throne is very interesting, but quite different in narrative style from previous books. Louis Wu and Chmeee are characters, but not the main ones, who are mostly Ringworld natives.
In his anthology “All the Myriad Ways” Niven talks about giving a talk at a Boston sf con (Boskone? Prob. not Arisia)and a lot of MITSFS members were chanting “Ringworld is unstable!” There probably weren’t 2000 of them – the MIT Science Fiction Society doesn’t have that many members (I am one – they have the best sf library around. The official index is the “Pinkdex” named after Marilyn “Fuzzy” Pink, who ended up with the ultimate collectible – she married Larry Niven.)
I’ve never tried to analyze it myself, but it seems likely that Ringworld IS unstable. Larry Niven evidently thought so, because, as pointed out above, he wrote in correction jets into the first sequel, “The Ringworld Engineers”. The jets are an essential element of the story, in fact, and not a throwaway device.
Sho’nuff, but there’s a difference between a slow-moving “vertical” ring, as Saturn’s would be if they were solid, and a rapidly-moving “ribbon.” Niven assumed that the shape coupled with the high velocity of rotation would negate Maxwell’s numbers. They do, to a certain degree, but not completely.
40% as dense as neutron star matter?! That would mean it would weigh, what, as much as both Magellanic Clouds combined? Maybe half as much as the whole damn Milky Way?!
